Selection Diversity

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples. Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability. Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.

The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.